The expression of cardiovascular disease processes, such as myocardial failure and hypertension, appear to involve membrane alterations which are poorly understood. These alterations may reflect changes in protein-lipid and protein-lipid-protein interactions in cell membranes that result in aberrant responsiveness to hormones and neurotransmitters and abnormal permeabilities of cations, particularly calcium. These interactions, however, remain poorly understood. In this regard, recent studies suggested that the cardiac glycoside, ouabain, alters the binding of calcium, sodium and potassium to phospholipids in a highly-purified Na ion, K ion-ATPase preparation, derived from the oyter medulla of sheep kidney. The specific objectives of this proposal are (a) to define the relationship between the Na ion, K ion-ATPase and cation binding to membrane receptor systems are interrelated in certain membrane settings through protein-lipid-protein interactions. Techniques and approaches, which would be employed, include: measurements of calcium binding versus pH, temperature and series of monovalent and divalent cations: induction of different conformational states of the Na ion, K ion-ATPase; changes in phospholipid/Na ion, K ion ATPase and composition of membrane lipids; assessment of interdependence between Na ion, K ion-ATPase molecules; hydribization of other receptor systems, including adenylate cyclase, into the Na ion, K ion-ATPase preparation and tests for possible interdependences of the systems; fluorescence spectra of lipid analogues incorporated into the Na ion, K ion-ATPase preparations and of fluorescence probes which bind to membrane surfaces.